Preparation of rolled sheets of smokeless powder



PREPARATION OF ROLLED SHEETS OF 1 SMOKELESS POWDER Alphens M. Ball, Wilmington, DeL, 'assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army No I Drawing. Continuation 'of application Serial No. 195,123, November 10, 1950. This application August 15, 1956, Serial No. 604,287

'5 Claims. (Cl. 18-'55) mechanical strength in order to eliminate powder brealo.

up and loss with resultant lowering of velocity.

An object of the invention is, accordingly, the preparation of high mechanical strength rolled sheets of smokeless powder. The high strength is obtained by rolling the sheets while wet with volatile solvents such as acetone and alcohol. fore the preparation of rolled sheets of smokeless powder of high mechanical strength by rolling powder wet with a volatile non-aqueous solvent. Other objects will appear.

hereinafter.

United States Patent A second object of the invention is there- In broad outlines the process of the instant invention comprises the following steps: Y (1) .Mixing ingredients in a sigma-blade mixer with the required. amount of acetone and alcohol solvent;

(2) Rolling solvent powder on rolling mills to obtain a snioothsheet with a minimum loss of solvent,

('3) Drying the sheets to a total volatile content of less than 0.50%.

The following examples are set forth to represent the invention, results obtained from other processes being included byway of contrast:

EXAMPLE 1 The powder used for this experiment was of the following composition:

Table l v 7 Percent Nitrocellulose 52.15 Nitroglycerine V 7 43.00 Diethylphthal-ate 3.00 Potassium nitrate 1.25 Diphenylamine 0.60

Some of material was processed by rolling solvent wet powder "on warm even-speed rolls and drying the rough sheets obtained in a forced air dry. The product obtained by this process was brittle and undesirable.

.EXAMPLE 2v Another part of the powder bf the previous example was treated by a second process which comprised extruding solvent powder into Ai-inch strands, cutting the strands intodiscs 0.01 thick, drying and rolling the dried discs onwarm even-speed rolls. The'sheets obtained by this Patented Oct. 6, 1959 f) Ice 2,907,073

7 EXAMPLE 3 A third portion of the powder of Example 1 was mixed and treated by the process of the present invention. The nitrocellulose was dehydrated with alcohol in a hydraulic press and mixed with nitroglycerine and acetone in a Schrader bowl. This premixed material was then mixed in asigma-blade mixer along with the other ingredients for 3 hours. The solvent content was approximately 20 parts of solvent per 100 pounds of powder, consisting of approximately a 48-52% mixture of acetone and alcohol. The solvent wet powder was removed from the mixer and rolled on cold (60-120 F.) even-spaced rolls until a smooth sheet was obtained. The sheets obtained were dried in .a forced air dry by circulating air at 110 F. for 24 hours and air at 125 F. for 24 hours. The dried sheets were tough and flexible and were far superior in mechanical strength to sheets prepared by a solventless process or the processes decribed in the two previous examples.

EXAMPLE 4 A series of powders were prepared by both a solvent and a solventless process for comparison of physical prop-' erties. The formulas for these powders are as follows:

The RDS number represents the designation of the batch. The solvent processed powders are designated below by .1 after the RDS number whereas the sol-ventless powders process were strong 'and' tough but much less so than that obtained by the next'procedure.

were designated by .2 after the RDS number;

The solventless powders were prepared as follows:

The water wet nitrocellulose was placed in a Schrader bowl and the dry chemicals added. The nitroglycerine was added to the mix and the completed charge was mixed for 15 minutes. 1 The water wet mix was then dried to approximately 8% moisture. The powder was then rolled o'n difierential rolls (1.5:1 ratio) at approximately 200 F. for 3 minutes and on even-speed rolls at 120 F. for 3 minutes.

In the preparation of the solvent powders the ingredients were mixed as in Example 3. Powder from the mixer was roller on even-speed rolls at F. and the sheets were dried in a forced air dry for 48 hours at F.

The sheets prepared by the solvent process were strong and flexible whereas the sheets prepared by the solventless process were brittle and weak. The results of physical tests were shown in the following table:

; V I Table III TENSILE STRENGTH LBS./IN-.?

From these values, it can be seen that not only is a 3 stronger product obtained by the solvent process but also that the sheet is less brittle as indicated by the limit of tensile strain test.

EXAMPLE 5 Another formula was made by both a solvent and a solventless process and the mechanical strengths were compared. 'The formula for these two powders is as follows:

The solventless process consisted of mixing the ingredients in a water slurry, filtering on a suction filter, and drying to approximately 8% moisture. The rolling of the solventless powder was the same as Example 4.

The solvent process consisted of mixing the ingredients as in Example 3. The solvent wet powder from the mixer was rolled 1.5 minutes on cold (70 F.) difierential rolls and then rolled on cold (100 F.) even-speed rolls to obtain a smooth sheet. The sheets were then dried for 48 hours at 120 F. in a forced air dry.

As in previous examples the solvent process powder was much superior in mechanical strength to the solventless powder. The comparative values are as follows:

Table V Solvent Process Tensile Strength, lbs/in. Strain at the Breaking Point, in Shear Strength, lbs/in. Impact Value, in. lb./in.

These values indicate the solvent process powder is far superior in mechanical strength to the solventless powder.

EXAMPLE 6 Two formulas were processed as in Example 3 i.e. by even-speed rolling only. Powders of the same formula were also prepared as in Example 2 with both differential and even-speed rolling.

The compositions of these powders are as follows:

The following table shows a comparison of the physical properties of the rolled sheets:

Table VII Difierential and Even-Speed Roll- Even-Speed Rolling ing Only Tensile Strain at Tensile Strain at Strength, Breaking Strength, Breaking lbs/in. Point, in. lbs/in. Point, in.

RDS 2075.1... 1, 595 '0. 250 RDS 2075.2; 1, 868-; 0.417 RDS 2077.1..- 1, 956 0.44 RDS 2077.2- 1, 426 0.502

4 This table shows that there is very little difference between the products obtained from the two types of rolling.

EXAMPLE 7 Three hundred pounds of powder were mixed as in Example 3. The composition of this powder was as follows:

Table VIII Percent Nitrocellulose (13.25% N) 52.15 Nitroglycerine 43.00 Diethylphthalate 3.00 Diphenylamine 0.60 Potassium nitrate 1.25

The solvent wet powder was taken from the mixer and rolled on differential rolls for diiferent lengths of time at various roll temperatures. The differential-rolled sheets were then rolled on even-speed rolls at F. until a smooth sheet was obtained. The sheets from the different conditions were analyzed for total volatile content and, after drying to less than 0.5% total volatile content, samples were analyzed for physical properties. The results of these tests are as follows:

Table IX PHYSICAL PROPERTIES AFTER DRYING TO LESS THAN 0.5% TOTAL VOLATILE CONTENT Powder Diff. Diff. T.V. T.V. Tensile Exten- Desig Roll Roll Diff. E.S. Strength, sion At nation Time Temp., Sheets, Sheets, lbs/in. Break,

(Min.) F. percent percent in.

The values for this same formula powder prepared by the solventless process in Example 4 are 650 lbs/in. and 0.247 in. for tensile strength and extension at break respectively. This data indicates that the mechanical strength of the sheet powder is dependent on the amount of solvent remaining in the powder after rolling and is independent of the rolling temperature alone. 'It should be noted that even the weakest powder was considerably stronger than that prepared by the solventless process.

Thus the preferred range of solvent remaining in the sheet would be 8% or above.

From the foregoing examples it can be seen that the type or conditions of mixing are probably not important except that the ingredients should be well dispersed. It is preferable to use approximately 20 parts of solvent per 100 parts of dry powder although a suitable product could be obtained by using 10-30 parts. The solvent used in the examples comprised approximately a 5050 mixture of acetone and alcohol. This ratio is not critical and suitable results could be probably obtained using a range of 25:75 to 100:0 of acetone and alcohol. Other nitrocellulose swelling solvents could also probably be substituted with comparable results. As shown by the examples, this process is applicable over a wide range of compositions.

As shown in Example 6 a suitable product can be obtained by employing either even-spaced rolls only or a combination of differential and even-speed rolls. The use of both types together is preferred because of the shorter rolling time required to obtain a smoothrsheet. The use of difierential-speed rolls alone did not give a smooth Sheet in any of the examples. Since the differential ratio was 1.5:1, rolling alone with a smaller ratio might result in anacceptablesurface. 7

As shown by Example 7, thetemperature of the rails is not critical. The rolling time at any given temperature is critical however since the solvent content of the powder after rolling has an eifect on the physical properties of the powder. It can be stated generally that the solvent content of the powder after rolling should exceed 8% for optimum results. The preferred range of conditions for rolling are as follows:

(1) A: to 1 /2 minutes on differential speed rolls at a temperature of 60120 F.;

(2) 515 passes on even-speed trolls at a temperature of 60-120 F.

The final step in the instant process has been carried out in a forced air dry. Any method of drying which is not too rapid would be acceptable.

This case is a continuation of my application Serial No. 195,123 filed November 10, 1950, and now abandoned.

What I claim is:

1. The method of preparing smokeless powder sheets of high tensile strength which comprises mixing a powder formulation containing a major proportion of nitrocellulose and nitroglycerine and a minor proportion of a member chosen from the group consisting of dinitrotoluene and trinitrotoluene with a volatile non-aqueous solvent in the proportion of 20 parts of solvent per 100 pounds of powder and chosen from the group consisting of acetone and mixtures thereof with alcohol, rolling the wet mixture on a rolling mill at a temperature of from 60 to 120 F. to obtain a smooth sheet having a solvent content of about 8-25 percent and drying the sheets to a total volatile content of less than 0.5 percent.

2. The method of preparing smokeless powder sheets percent of the weight of the formulation, rolling the wet of high tensile strength which comprises mixing a powder formulation comprising as its explosive components about acetone and mixtures thereof with alcohol, the weight of said solvent comprising from about 20 to about 30 mixtures on a rolling mill at a temperature of from to 120 F. to obtain a smooth sheet having a solvent content of about 8 to 25 percent, and drying the sheets to a total volatile content of less than 0.5' percent.

3. The method of preparing smokeless powder sheets of high tensile strength which comprises mixing a powder formulation containing a major proportion of nitroglycerine and nitrocellulose with a volatile non-aqueous solvent chosen from the group consisting of acetone and mixtures thereof with alcohol, the weight of said solvent comprising from about 20 to about 30 percent of the weight of the formulation, rolling the wet mixture at a temperature of from 60 to 120 F. to obtain a smooth sheet with a solvent content of about 8 to 25 percent and subsequently drying the sheets to a total volatile content of less than 0.5 percent.

4. The method of claim 3 in which the volatile nonaqueous solvent consists of a 50:50 mixture of acetone and alcohol.

5. The process of preparing sheets of smokeless powder of high mechanical strength which comprises mixing the desired powder formulation with a volatile, nonaqueous solvent consisting of a mixture of alcohol and acetone in proportions of 10 to 30 parts by weight of solvent to parts of the dry powder, rolling the wet mixture on a rolling mill to obtain a smooth sheet having a solvent content of from 8 to 25 percent and drying the sheets to a total volatile content of less than 0.5 percent.

References Cited in the file of this patent UNITED STATES PATENTS 1,978,070 York Oct. 23, 1938 2,210,871 Boddicker Aug. 6, 1940 2,417,090 Silk et a1. Mar. 11, 1947 2,668,132 Baker Feb. 2, 1954 2,691,192 Bent Oct. 12, 1954 

1. THE METHOD OF PREPARING SMOKELESS POWDER SHEETS OF HIGH TENSILE STRENGTH WHICH COMPRISES MIXING A POWDER FORMULATION CONTAINING A MAJOR PROPORTION OF NITROCELLULOSE AND NITROGLYCERINE AND A MINOR PROPORTION OF A MEMBER CHOSEN FROM THE GROUP CONSISTING OF DINITROTOLUENE AND TRINITROTOLUENE WITH A BOLATILE NON-AQUEOUS SOLVENT IN THE PROPORTION OF 20 PARTS OF SOLVENT PER 100 POUNDS OF POWDER AND CHOSEN FROM THE GROUP CONSISTING OF ACETONE AND MIXTURES THEREOF WITH ALCOHOL, ROLLING THE WET MIXTURE ON A ROLLING MILL AT A TEMPERATURE OF FROM 60* TO 120* F. TO OBTAIN A SMOOTH SHEET HAVING A SOLVENT CONTENT OF ABOUT 8-25 PERCENT AND DRYING THE SHEETS TO A TOTAL VOLATILE CONTENT OF LESS THAN 0.5 PERCENT. 